THE DISTRIBUTION, AVAILABILITY, AND PERSISTENCE OF MERCURY IN SEDIMENTS OF AN URBAN STREAM

Mercury (Hg) is a toxic and persistent pollutant that can result in exposure risk even at low levels given its bioaccumulation potential. In aquatic systems a large fraction of Hg is present in the sediments due to the strong affinity of Hg to sorb on surfaces. Depending on the physical and chemical conditions of the environment sediments can act as both sinks and sources of Hg. Thus, the majority of uptake for Hg is related to sediment methylation potential and biotic contact with sediments. Sediments are also important in the transport of Hg and MeHg, mainly during storm events when Hg-bound sediments are mobilized and reintroduced into the water column. However, the presence of urban activities results in additional sources of Hg to the streams and shifts in the environmental conditions that alter both the bioavailability and mobilization of Hg. The present study examines the shifts in the fate and transport of Hg in stream sediments of an urban watershed. Grab sediment samples were collected across the Park River watershed in Hartford, CT, to characterize the distribution of Hg through a series of chemical analysis including total and methyl Hg (THg, MeHg), organic carbon (OC), inorganic C, total C, total S, total H, select trace metals (Cu, Pb, Zn), acid volatile sulfide (AVS), and chromium reducible sulfide (CRS). Additionally, suspended sediment samples were collected using suspended sediment collectors constructed in the laboratory. Such collectors were installed in six sampling locations across the watershed over four three-month periods. Suspended sediment samples were characterized through the same series of analysis mentioned above, and were further analyzed for the 16 EPA priority pollutant PAHs and select quaternary ammine compounds (QACs). Such extensive analytical analysis was performed to identify the different sources of sediment entering the stream through principal component analysis (PCA). Finally, the bioavailability of Hg in both grab and suspended sediment samples was assessed through selective sequential extractions and biouptake experiments in benthic invertebrates.